Person:

Zegura, Ellen W.

Permanent Link

https://hdl.handle.net/1853/71879

Associated Organization(s)

Organizational Unit

School of Computer Science

Full item page

Publication Search Results

Now showing 1 - 10 of 21

Fast Packet Classification with a Varying Rule Set

(Georgia Institute of Technology, 2001) Merugu, Shashidhar ; Gummalla, Ajay Chandra V. ; Sala, Dolors ; Zegura, Ellen W.

Multi-dimensional packet classification is increasingly important for applications ranging from fire-walls to traffic accounting. Fast link speeds, the desire to classify with fine granularity, and the need for agility in a dynamic environment all pose significant challenges for packet classification. We propose an approach that is capable of handling a changing set of classification rules that span multiple fields. Our approach is based on extracting a relatively small set of bits that uniquely identify the packets satisfying each rule. Changes to the rule set are handled in-line via a fast update mode that adds to the rule table, while a background process performs reoptimization of the full rule table less frequently. The classification process can be efficiently implemented using pipelined hardware and supports high packet arrival rate.
Efficient Routing Using NIx-Vectors

(Georgia Institute of Technology, 2001) Riley, George F. ; Ammar, Mostafa H. ; Zegura, Ellen W.

We introduce the concept of Neighbor-Index Vector (NIx-Vector) routing which gives efficient and consistent routing of packets in Internet routers. A NIx-Vector is a compact representation of a routing path, which is small enough to be included in a packet header. We show how, by including the routing information in the packet header, routing decisions can be made in O(1) time at each router, with no caching or state in the routers (other than the existing routing tables). The creation of a NIx-Vector for a source and destination pair requires one round trip time, but once the NIx-Vector is known, it can be retained by the source and reused indefinitely with no further setup time required (or until it becomes no longer valid, which is easily detected). In addition to O(1) routing decisions, the use of NIx-Vectors to record and specify routes has other benefits. NIx-Vectors provide for route pinning which is beneficial for reservation protocols and mitigates the effect of routing flaps on long lived flows. A variation of NIx-Vectors can insure symmetrical routes from a source to a destination and back to the source, which is also beneficial to some reservation protocols. We give a complete description of how NIx-Vectors are created and used in Internet routers; and give empirical data showing the number of bits required to represent NIx-Vectors for typical Internet paths
An Evolutionary Framework for AS-Level Internet Topology Modeling

(Georgia Institute of Technology, 2001) Gao, Ruomei ; Zegura, Ellen W.

Models for network topology form a crucial component in the analysis of protocols. This paper systematically investigates a variety of evolutionary models for autonomous-system (AS) level Internet topology. Evolution-based models produce a topology incrementally, attempting to reflect the growth patterns of the actual topology. While evolutionary models are appealing, they have generally agreed less closely with measurements of real data than non-evolutionary models. We attempt to understand what contributes to a "good" evolutionary model. Our systematic study consists of a relatively generic evolutionary model framework, which we populate with different choices for the components. This allows us to compare a variety of instances of models to measurements from real data sets. We study issues such as the initial topology, the type of preferential connectivity used in adding edges, and the role of "growth" edges added between existing nodes. We find that appropriate instantiation of the framework can provide topologies that agree closely with real data. We also use our work to highlight several crucial open problems in topology modeling.
Selecting Among Replicated Adaptive Multicast Servers

(Georgia Institute of Technology, 2000) Ammar, Mostafa H. ; Zegura, Ellen W. ; Fei, Zongming

Server replication and multicasting are well-established techniques for increasing capacity of a networked service and improving client performance. In this paper, we consider the combination of these two techniques. Specifically, we investigate the problem of selecting amongst rate-adaptive multicast servers, which adjust their sending rate based on network conditions and/or feedback from clients. Effective server rate adaptation can lead to efficient utilization of network resources and performance improvement perceived by clients. In this initial study of adaptive multicast server selection, we explore some fundamental issues and study the implications of different selection strategies on the performance perceived by clients. We first define the Static Multicast Selection Problem, in which there are static sets of clients and servers, and one needs to establish a set of multicast trees with one tree for each server. We explore several optimization problems based on different performance measures. We prove that the general problem is NP-hard and then present two interesting special cases with an optimal polynomial-time solution in each case. We design a heuristic for the general case and show that it can improve the performance over some simple strategies. We also consider the Dynamic Multicast Selection Problem, in which clients may join and leave multicast trees already established. We design a heuristic for this dynamic case by which clients can select a tree to join. We investigate the performance of the heuristic through simulation.
Efficient Routing using NIx-Vectors

(Georgia Institute of Technology, 2000) Ammar, Mostafa H. ; Zegura, Ellen W. ; Riley, George F.

We introduce the concept if NIx-Vector routing which gives efficient and consistent routing of packets in Internet routers. A NIx-Vector is a compact representation of a routing path, which is small enough to be included in a packet header. We show how, by including the routing information in the packet header, routing decisions can be made in O(1) time at each router, with no caching or state in the routers (other than the existing routing tables). The creation of a NIx-Vector for a source and a destination pair requires one round trip time, but once the NIx-Vector is known, it can be retained by the source and reused indefinitely with no further setup time required (or until it becomes no longer valid, which is easily detected.) In addition to O(1) routing decisions, the use of NIx-Vectors to record and specify routes has other benefits. NIx-Vectors provide for route pinning, which is beneficial for reservation protocols and mitigates the effect of routing flaps on long lived flows. A variation of NIx-Vectors can insure symmetrical routes from a source to a destination and back to the source, which is also beneficial to some reservation protocols. Another variation of NIx-Vectors can insure that all packets from the same flow take the same path, even in the presence of redundant paths or links, which will reduce the frequency of pack misordering. Finally, the NIx-Vector concept can be combined with probabilistic packet market to allow for the reconstruction of a complete routing path for packets of unknown origin, which is useful in determining the source of denial of service security attacks. We give a complete description of how NIx-Vectors are created and used, and describe an end-to-end protocol for managing NIx-Vectors. We give empirical data showing the number of bits required to represent NIx-Vectors for typical Internet paths. We give a proposed IPv4 option which will allow for a simple implementation.
On Scalable QoS Routing: Performance Evaluation of Topology Aggregation

(Georgia Institute of Technology, 1999) Hao, Fang ; Zegura, Ellen W.

A number of important questions remain concerning the scalability of networks with quality of service guarantees. We consider one of these questions: can QoS routing scale to large networks? To address this question, we evaluate performance of four QoS routing algorithms both with and without topology aggregation, based on simulations of relatively large, structured networks. Among our observations, we find --- contrary to intuition --- that topology aggregation does not always have a negative impact on routing performance. Aggregation can reduce the routing information fluctuation, increase stability, and thus benefit routing performance. We also propose two new methods of aggregating routing information. Our hybrid aggregation method has performance much better than conventional star aggregation and approaches unaggregated performance. Our weighted aggregation method, while intuitively appealing, offers mixed performance across topologies.
Optimal Allocation of Clients to Replicated Multicast Servers

(Georgia Institute of Technology, 1999) Ammar, Mostafa H. ; Zegura, Ellen W. ; Fei, Zongming

Server replication is an approach that is often used to improve the scalability of a service. One of the important factors in the efficient utilization of replicated servers is the ability to direct client requests to the `best" server, according to some optimality criteria. Recently, there have been several proposals for multicast services in which a server delivers information to multiple clients simultaneously. Such proposals include multicasting of web content, multicast-based video services (on-demand and pay-per-view style services), multicasting of database content and broadcast disks. The goal of many of these proposals is to use multicast to enhance the ability of the service to handle a large number of clients economically. Multicast servers may be replicated for several reasons: to distribute the load among on-demand multicast servers, to balance the `feedback" load on the servers or on entities along the multicast tree from the servers, or to select the server that is at the root of the `best" multicast routing tree. In this paper we first give a definition of the static multicast server selection problem, in which we assume a set of static clients and multicast servers and consider how one might produce an optimalallocation of the clients to the servers. We propose a transformation method for deriving multicast server selection algorithms from the traditional multicast routing algorithms. To investigate the dynamic behavior of client join and leave and the cost incurred during the process, we next define the dynamic multicast server selection problem, in which the potential clients join and leave the multicast session dynamically, and the goal is to produce an optimal allocation of clients to servers with an emphasis on how this allocation behaves over time. We formulate the problem as a Markovian Decision Process (MDP) and analyze the tradeoff between the cost of the multicast tree(s) and the transition cost of establishing and removing links from the tree(s). We also explore the effect of join/leave frequency on optimal policy. Our analysis leads to two heuristics which we use to propose a selection algorithm. The algorithm uses a very simple join and leave strategy yet still can generate low cost trees. Our simulation compares the performance of our proposed algorithm with various other multicast server selection algorithms.
Inter-Receiver Fair Multicast Communication over the Internet

(Georgia Institute of Technology, 1999) Zegura, Ellen W. ; Ammar, Mostafa H. ; Jiang, Tianji

Multicast protocols target applications involving a large number of receivers with heterogeneous data reception capabilities.To accommodate heterogeneity, the sender may transmit at multiple rates, requiring mechanisms to determine the rates and allocate receivers. In this paper, we develop a protocol to control the rate of a multicast session, with the goal of maximizing the inter-receiver fairness, an intra-session measure that captures the collective "satisfaction" of the session receivers. Our target environment is the Internet, where fair sharing of bandwidth must be achieved via end-system mechanisms and fairness to TCP is important. We develop and evaluate protocols to maximize this measure by maintaining a fixed-rate base group and a variable-rate group. We show that our schemes offer improvement over single-rate sessions, while maintaining TCP-friendliness.
Scalability Techniques in QoS Routing

(Georgia Institute of Technology, 1999) Hao, Fang ; Zegura, Ellen W.

One barrier to deployment of large-scale QoS networks is scalability of QoS routing. Two major sources of overhead incurred by QoS routing are frequent network state updates and QoS-based path computation. Researchers have proposed an impressive array of techniques to reduce these overheads. The goal of this paper is to survey scalability techniques, in the context of a taxonomy intended to illustrate the relationships between different approaches and highlight areas of open research. We also include selected performance results from our own work, to demonstrate the inherent tension between scalability and performance. Our results are obtained using simulations of networks with up to 200 nodes; such large topologies are critical for fully evaluating scalability techniques.
Hashing-Based Traffic Splitting Algorithms for Internet Load Balancing

(Georgia Institute of Technology, 1999) Cao, Zhiruo ; Wang, Zheng ; Zegura, Ellen W.

Replication of resources is a key technique for improving Internet performance. Effective use of replicated resources requires good load distribution schemes. We study the performance of several hashing schemes for distributing traffic while preserving the order of packets within a flow. Traffic distribution with per-flow ordering has applications that include balancing traffic across multiple Internet access links and balancing HTTP request load in a web server farm. While hashing schemes for load balancing have been proposed in the past, this is the first comprehensive study of performance using real traffic traces. We evaluate five direct hashing methods and one table-based hashing method. We find that hashing using a 16-bit CRC over the TCP five-tuple gives excellent load balancing performance. Further, load-adaptive table-based hashing using the exclusive OR of the source and destination IP addresses achieves comparable performance to the 16-bit CRC. Table-based hashing can also distribute load according to unequal weights. We also report on four other schemes with poor to moderate performance.